Known in the automotive industry, for example, are trim pieces manufactured by a process of injection molding of polymeric materials such as thermoplastics such as polyvinyl chloride (PVC), or thermosetting materials such as the terpolymer of ethylene propylene diene monomer (EPDM), etc.
Such a trim piece is known to be provided with an outer laminar film or skin for decorative and/or protective purposes. Such films are typically of polyvinyl chloride or a fluorinated polyolefin, and may be multi-layered.
A typical method of manufacturing such a trim piece involves injecting molten PVC into a cavity mold behind a film held in a mold cavity about its edges. The film is forced by the molten material into abutment with the face of the mold cavity to take on the three-dimensional pattern of the face of the mold. Because the film is secured within the mold about its edges, the filmn stretches unevenly during formation of the piece. Such stretching often leads to an aesthetically undesirable appearance of the final product. Further, it is generally not practicable to wrap the film edge behind onto the rear face of the injection-molded portion of the piece using this approach.
Another method of manufacturing a trim piece involves injecting molten material into a cavity behind a pre-formed rigid or semi-rigid film located in the cavity. This approach thus requires the film to be shaped in a separate step, as for example, by vacuum forming prior to the injection molding step and the film to be rather carefully located in the mold cavity for proper formation of the piece. The film portion must also be trimmed at some point.
It is generally desirable for the film of such pieces to wrap behind onto the rear surface of the injection-molded substrate of the piece. In the context of this invention, we refer to a trim piece in which at least edges of the film are wrapped onto the rear surface of the substrate as an "edge-wrapped" piece. Such edge-wrapped pieces can be desirable, for example, because once such a piece is installed on an automobile and the rear surface is concealed, lack of access to the edge of the film lessens the likelihood of film delamination.
Aesthetically, edge-wrapped pieces can be desirable as the underlying substrate is unexposed. The underlying injection-molded portion might have a less pleasing appearance than the film. This would be the case, for instance, where the substrate is of low-grade injection-molded PVC and the film is a high-quality laminate. Further, in the industry today, it is desirable to use recycled material wherever possible. An unexposed underlying substrate presents such an opportunity.